Absolute value circuit

Abstract

An absolute value circuit capable of providing, through an output terminal, a signal corresponding to the absolute value of the difference between a first input signal and a second input signal, comprises a first circuit, a second circuit and a uni-directional circuit. The first circuit is adapted for subtracting a current corresponding to said second input signal from a current corresponding to said first input signal and for supplying to said output terminal a current of one direction corresponding to the result of said subtraction in case said result is positive, or a current of the other direction corresponding to the result of said subtraction in case said result is negative. The second circuit is adapted for subtracting a current corresponding to said first input signal from a current corresponding to said second input signal and for supplying to said output terminal a current of one direction corresponding to the result of said subtraction in case said result is positive, or a current of the other direction corresponding to the result of said subtraction in case said result is negative. The uni-directional circuit is adapted for transmitting either one of said current of said one direction and said current of said the other direction supplied from said first and second circuit.

We claim: 
     
       1. An absolute value circuit capable of providing, through an output terminal, a signal corresponding to the absolute value of the difference between a first input signal and a second input signal, comprising: (a) first circuit means adapted for subtracting a current corresponding to said second input signal from a current corresponding to said first input signal, and for supplying to a first terminal a current corresponding to the result of said subtraction of a first direction in case said result is positive, and for supplying a current corresponding to the result of said subtraction of a second direction opposite to said first direction in case said result is negative;   (b) second circuit means adapted for subtracting a current corresponding to said first input signal from a current corresponding to said second input signal and for supplying to a second terminal a current corresponding to the result of said subtraction of said first direction in case said result is positive, and for supplying a current corresponding to the result of said subtraction of said second direction in case said result is negative; and   (c) uni-directional circuit means disposed between said first and second terminals and said output terminal for transmitting current of only a predetermined one of said first and second directions from said first and second circuit means to said output terminal.   
     
     
       2. An absolute value circuit according to claim 1, wherein each of said first and second circuit means comprises a differential amplifier composed of a first amplifier for receiving said first input signal and a second amplifier for receiving said second input signal; and a constant current source for biasing said differential amplifier. 
     
     
       3. An absolute value circuit according to claim 2, wherein each of said first and second circuit means further comprises a current mirror circuit containing a current master circuit and a current slave circuit and functioning as a load to said differential amplifier, wherein the first and second amplifiers of said first circuit means are respectively connected to an associated current master circuit and to an associated current slave circuit, while the second and first amplifiers of said second circuit means are respectively connected to an associated current master circuit and to an associated current slave circuit, thereby achieving a push-pull function by each differential amplifier and its associated current slave circuit. 
     
     
       4. An absolute value circuit according to claim 3, wherein said uni-directional circuit means comprises two uni-directional current circuit elements which are connected at one end thereof respectively to the first and second terminals, the first and second terminals constituting respective junction points between said differential amplifiers and said current slave circuits in said first and second circuit means, said uni-directional current circuit elements being connected in such a manner as to pass current of said predetermined one direction resulting from said push-pull function, and which uni-directional current circuit elements are connected in common at another end. 
     
     
       5. An absolute value circuit according to claim 4, wherein said uni-directional circuit means comprises a current-voltage converter for converting, into a voltage, a current obtained at the common connecting point of said two uni-directional current circuit elements. 
     
     
       6. An absolute value circuit according to claim 3, wherein said uni-directional circuit means comprises two additional current mirror circuits each containing a current master circuit and a current slave circuit, said current master circuits of the additional current mirror circuits being respectively connected to junction points between said differential amplifiers and said first-mentioned current slave circuits in said first and second circuit means in such a manner as to pass current of said predetermined one direction, and said current slave circuits of said two additional current mirror circuits being commonly connected to said output terminal.